The structure of the esters of formula (I) in racemic form is known. Several references have disclosed it, either mentioning only the molecule, or describing its preparation in detail. In this context, the following references can be cited for their mention of the compound of formula (I) wherein X represents a C.dbd.O group, namely 3-methyl-2-oxo-ethyl pentanoate: R. Kozlowski et al., Org. Prep. Proceed. lnt., 21(1), 75-82 (1989); Y. Akiyama et al., Chem. Pharm. Bull. 32(5), 1800-1807 (1984); Y. Akiyama et al., Chem. Lett. 8, 1231-1232 (1983); P. Yates et al., Can. J. Chem. 61(7), 1397-1404 (1983); H. M. Walborsky et al., J. Org. Chem. 39(5), 604-607 (1974); L. N. Akimova et al., Zh Org. Khim. 5(9), 1569-1571 (1969). However none of these references either describes the odor of said ester or suggests its utilization in the field of perfumery.
Moreover, the acids of formula ##STR4## wherein R can be hydrogen or represents a great variety of alkyl radicals, saturated or unsaturated, linear or branched, and namely 3-methyl-2-oxopentanoic acid, are known to be used in the field of flavors. The international application WO 96/10927 describes the utilization of this group of compounds in a variety of foods, to which they impart an enhanced impact in the mouth. The C.sub.1 to C.sub.4 alkyl esters of said acids are also mentioned as useful flavoring ingredients in a general manner, without however giving any concrete example of preparation or even of application of these alkyl esters. Once again there is no description of the odor characteristics of said esters.
On the other hand, the racemic compound of formula (I) wherein X represents a CH--OH group, namely ethyl 2-hydroxy-3-methylpentanoate is described in the following articles: R. Kaiser, J. Ess. Oil Res. (1991), 3, 129-146 or R. Kozlowski, Z. Kubica, B. Rzeszotarska, L. Smelka, G. Pietrzynski, Org. Prep. Proced. Int. (1989), 21(1), 75-82. Moreover, the synthesis of one of the four optically active isomers of this compound, namely ethyl (2S,3S)-2-hydroxy-3-methylpentanoate has been described by D. Wistuba, O. Trager and V. Schurig in Chirality (1992), 4(3), 185-92. However, this article does not include any description of the organoleptic properties of said isomer and generally speaking, the prior art never suggests any possible usefulness of the isomers of 2-hydroxy-3-methyl-pentanoate from an olfactory point of view.